This is my Cushcraft XM-240 "Big Thunder" yagi I use for 40 meters here at W4MY. It is up at 73 feet on a Rohn 25 tower fed with Beldon 9913-F7 coaxial cable. I turn it with a Ham IV rotor nested in the tower on a chrome-molly pole 2-1/16" in diameter.
This is certainly not a "beginner's" antenna. It takes allot of work to get it in the air, but worth every minute of it. Even at this point in the sunspot cycle (dead low) I hear DX on 40 just about whenever I turn the radio on.
As you can see in the picture, it is a two element design with a driven element in the front, and a reflector at the rear. It has an inductor 3/4 the distance away from the center to help reduce the length and a capacitance hat near the end of each of the elements. I don't know much about the use of capacity hats except that they help increase the radiation resistance of an electrically short antenna thus increasing the efficiency. I can actually say they got it right, its performance is outstanding!
I did make a couple of structural changes to the original design to make it better able to withstand the elements long term. I beefed up the truss system by replacing the truss bracket with a steel one I fabricated. The aluminum one just didn't have the look of "long term" to it. I also put a stainless steel eye bolt at the two ends of the boom to hold the truss guy, again, Cushcraft's design was a little wimpy.
In the one year it has been up (or just shy of a year) it has performed magnificently. I'm glad I got it.
73 to all Marty / W4MY
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